With the emerging of World Interoperability for Microwave Access (WiMax), a third-generation mobile communication system must improve network performance and reduce costs of network construction and operation in order to keep strong competitiveness in the field of mobile communications. Therefore, a standardization working team of a 3rd Generation Partnership Project (3GPP) is committed to studying the evolution of a Packet Switch Core (PS Core) network and a Universal Mobile Telecommunication System Radio Access Network (UTRAN) at present. The subject of the study is referred to as System Architecture Evolution (SAE), and the purpose of the study is to enable an Evolved Packet Core (EPC) network to provide a higher transmission rate and shorter transmission delay, optimize grouping and support mobility management among an Evolved UTRAN (E-UTRAN), a Universal Terrestrial Radio Access Network (UTRAN), a Wireless Local Area Network (WLAN) and other non-3GPP access networks.
At present, the architecture of SAE, as shown in FIG. 1, includes the following network elements: an Evolved Radio Access Network (E-RAN), a Packet Data Network (PDN), an E-Packet Core (EPC) network, a Mobility Management Entity (MME), an SGW, a PDN Gateway (PGW), a Policy and Charging Rules Function (PCRF) entity, a Home Subscriber Server (HSS), and a Charging Gateway Function (CGF) entity.
The E-RAN can provide a higher uplink/downlink rate, lower transmission delay and more reliable radio transmission. A network element contained in the E-RAN is an Evolved NodeB (eNodeB), which is used to provide radio resources for the access of User Equipment (UE).
The PDN is used for providing services to a UE.
The EPC network provides lower delay and allows the access of more radio access systems, and the EPC network contains following network elements:
The MME, which is a control plane function entity, serves as a server for temporarily storing user data, and is responsible for managing and storing context of UE (for example, a UE/user identifier, a mobility management state, a user safety parameter), allocating a temporary identifier to a UE and authenticating a UE when the UE stays in a tracking area or the network, processing all non-access stratum messages between the MME and the UE, and triggering the paging of SAE. The MME is the mobile management unit of the SAE system. In a Universal Mobile Telecommunications System (UMTS), the mobile management unit is a Serving General Packet Radio Service (GPRS) Support Node (SGSN).
The SGW, which is a user plane entity, is responsible for processing routing of user plane data, terminating downlink data of a UE in an idle (ECM_IDLE) state, and managing and storing SAE bearer context of a UE, such as IP bearer service parameter and internal network routing information. The SGW is an anchor point of user plane in 3GPP system and one UE has one SGW only at a time.
The PGW is responsible for a UE to access a PDN and allocates an IP address to the UE, and also is a mobility anchor point of 3GPP and non-3GPP access systems. The functions of the PGW further include policy enforcement and charging support. A user can access a plurality of PGWs at the same time. A Policy and Charging Enforcement Function (PCEF) entity also is located in the PGW.
The PCRF entity is responsible for providing policy control and charging rules to the PCEF.
The HSS permanently stores UE's subscription data. Contents stored in the HSS include International Mobile Subscriber Identification (IMSI) of a UE and an IP address of the PGW.
The CGF entity is responsible for collecting charging data of a user.
Physically, the SGW and the PGW can be merged into a whole entity. In the EPC system, the user plane network element includes the SGW and the PGW.
In the EPC system, the network may allocate a dynamic IP address to the UE or allocate a static IP address to the UE. As shown in FIG. 2, UE attach and the allocation of a static IP address during the attach procedure include the following steps:
Step 201: A UE sends an attach request message to an eNodeB, and the attach request message includes IMSI, UE network capability and other parameters.
Step 202: The eNodeB selects an MME for the UE and forwards the attach request message to the MME.
Step 203: The MME sends a location update request message to an HSS, and the location update request message includes an update type and an MME address.
Step 204: The HSS returns a location update response message to the MME, and the location update response message includes user data and the user data include an Access Point Name (APN), default bearer Quality of Service (QoS) and a corresponding static IP address.
Step 205: The MME selects an SGW for the UE according to location information of the UE, and sends a session establishment request message to the selected SGW. The session establishment request message includes an IP address and a Tunnel Endpoint Identifier (TEID) of the MME, a control plane IP address of the PGW, default bearer QoS, an EPS bearer ID, a static IP address etc.
Step 206: The SGW sends a session establishment request message to a PGW, and the session establishment request message includes an control plane IP address and a TEID of the SGW, a user plane IP address and a TEID of the SGW, the control plane IP address of the PGW, the default bearer QoS, the EPS bearer ID, the static IP address etc.
Step 207: The PGW returns a session establishment response message to the SGW, and the session establishment response message includes an IP address and a TEID of the PGW for the control plane, an IP address and a TEID of the PGW for user plane, bearer QoS and an IP address.
Step 208: The SGW returns a session establishment response message to the MME, and the session establishment response message includes the IP address and the TEID of the PGW for the control plane, the IP address and the TEID of the PGW for the user plane, IP address and the TEID of the SGW for the user plane, the bearer QoS, IP address of the UE etc.
Step 209: The MME sends an initial context establishment request message to the eNodeB, and the initial context establishment request message includes the IP address and the TEID of the SGW for the user plane, the bearer QoS, the EPS bearer ID, and an attach accept message. The attach accept message includes the APN, an IP address of the UE, Globally Unique Temporary Identity (GUTI), a Tracking Area Identity (TAI) list etc.
Step 210: The eNodeB sends a Radio Resource Connection (RRC) reconfiguration message to the UE and sends the attach accept message to the UE. The RRC reconfiguration message includes an EPS radio bearer ID.
Step 211: The UE sends a RRC configuration complete message to the eNodeB.
Step 212: The eNodeB sends an initial context establishment response message to the MME, and the initial context establishment response message includes an IP address and a TEID of the eNodeB for the user plane.
Step 213: The UE sends a direct transfer message to the eNodeB, and the direct transfer message includes an attach complete message.
Step 214: The eNodeB sends the attach complete message to the MME.
Step 215: The MME sends a bearer modification request message to the SGW, and the bearer modification request message includes the IP address and the TEID of the eNodeB for the user plane, and the EPS bearer ID.
Step 216: The SGW returns a bearer modification response message to the MME.
From the above descriptions, it can be seen that, when the new SGW is taken as the UE's SGW, a new SGW cannot learn the attribute of the UE's IP address in time. Therefore, a CGF entity connected with the new SGW cannot accurately charge the UE according to the attribute of the IP address.